Background: Nonunion of the humeral shaft can turn into bone defects. There is no consensus on the optimal treatment of humeral shaft nonunion with bone defects. Herein, we presented a single case of a patient with a 9.5 cm humerus shaft bone defect treated with a 3D printed Ti6Al4V microporous prosthesis after internal fixation failure of a middle-inferior humerus fracture.Case Description: A 53-year-old female who injured her left upper limb by falling was diagnosed with a fracture of the left humeral shaft. The fracture was treated with open reduction and internal fixation. Nine months postoperatively, radiography examination indicated humeral nonunion with a 9.5 cm segmental bone defect. A 3D printing technology was then used to design and fabricate a customized microporous prosthesis with an intramedullary nail and lateral plates. A two-stage surgical strategy was performed, including radical debridement, temporary fixation for the induced membrane formation, and the implantation of the prosthesis. At 18 months of follow-up, encouraging clinical outcomes were observed. The prosthesis remained stable in the original implantation area and callus formation was found at the contact end of the prosthesis and bone stump. The upper limb functions returned to normal with a satisfactory functional score. Also, no complications were found.Conclusions: Reconstruction with a 3D printed microporous prosthesis might be used as an alternative for the repair of large segmental bone defects of limbs.

Critical metaphyseal bone defects caused by nonunion and osteomyelitis are intractable to repair in clinical practice owing to the rigorous demanding of structure and performance. Compared with traditional treatment methods, 3D printing of customized porous titanium alloy prostheses offer feasible and safe opportunities in repairing such bone defects. Yet, so far, no standard guidelines for optimal 3D printed prostheses design and fixation mode have been proposed to further promote prosthesis stability as well as ensure the continuous growth of new bone. In this study, we used a finite element analysis (FEA) to explore the biomechanical distribution and observed new bone regeneration in clinical practice after implanting 3D printed prostheses for repairing metaphyseal bone defects. The results reflected that different fixation modes could result in diverse prosthesis mechanical conductions. If an intramedullary (IM) nail was applied, the stress mainly conducted equally along the nail instead of bone and prosthesis structure. While the stress would transfer more to the lateral bone and prosthesis’s body when the printed wing and screws are selected to accomplish fixation. All these fixation modes could guarantee the initial and long-term stability of the implanted prosthesis, but new bone regenerated with varying degrees under special biomechanical environments. The fixation mode of IM nail was more conducive to new bone regeneration and remodeling, which conformed to the Wolff’s law. Nevertheless, when the prosthesis was fixed by screws alone, no dense new callus could be observed. This fixation mode was optional for defects extremely close to the articular surface. In conclusion, our innovative study could provide valuable references for the fixation mode selection of 3D printed prosthesis to repair metaphyseal bone defect.